Mechanism for the control of strip materials



y 1959 R; w. TAYLOR ETAL 2,888,259

MECHANISM FOR THE CONTROL OF STRIP MATERIALS Filed Jan. 9, 1957 3Sheets-Sheet l MUKDOWUd TL .9

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Inventors, RONALD w. TAYLOR, by JAMES AUTHUR HUNTER ME MLUMV J24Attorney? y 1959 R. w. TAYLOR ET AL 2,888,259

MECHANISM FOR THE CONTROL OF STRIP MATERIALS Filed Jan. 9, 1957 3Sheets-Sheet 2 A s W/ /A W//////////// 5 W744 2 n N 1 v fl fl y W n v vv 3 4 u A wfl L 2M1! L, 7/// 4/ 2 3 T n G n. F

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RONALD W. TAYLOR by JAMES ARTHUR HUNTER 2mm, i fl-M'MZL MM 1; A t t o rn e yy May 26, 1959 Y -R. w. TAYLOR ETAL 2,888,259

MECHANISM FOR THE CONTROL OF STRIP MATERIALS Filed Jan. 9, 1957 3Sheets-Sheet 3 Q. O J (9 u. LL

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, Attorneys MECHANISM FOR THE CONTROL OF STRIP MATERIALS Ronald W.Taylor and James Arthur Hunter, Stevenage,

England; said Taylor assignor to W. H. Sanders (Electronics) Limited,Stevenage, England Application January 9, 1957, Serial No. 633,292

Claims priority, application Great Britain January 10, 1956 9 Claims.01. 271-22 This invention relates to mechanism for the control ofmovement of strip material, being of the kind where the moving strip isallowed to form a downward loop under gravity between two rollers or thelike and the position of the bottom of the loop is sensed by photoelectric means which control the speed of feeding either to or from theloop such that the loop is maintained a constant size irrespective ofwhether the speed of movement of the strip varies. An example of theabove kind of mechanism is the apparatus for feeding sheet steel stripinto a side trimming machine and a shearing machine for shearing thestrip into lengths. The shearing machine is, manually controlled todeliver the lengths of strip as required, and the control mechanism ofthe kind referred to is used to control the speed of rotation of thereel or other source of strip and the side trimmer in accordance withthe manually controlled speed of the shearing machine. For this purposetwo loops are provided, one between the source and the side trimmingmachine and another between the side trimming machine and the shearingmachine. The photo electric means on each loop controls the speed of thestrip into the loop. I

It is found that where the photo electric means senses theposition onlyof the bottom of the loop that the inertia of the strip and rollers andthe like associated with the feed are such that it is easily possiblefor the loop either to straighten out or to become excessively big withthe result that damage might occur to the apparatus or the strip.

The. object of the present invention is to provide a more accuratecontrol of strip movement in mechanism of the kind referred to than hashitherto been the case.

In accordance with the present invention in a mechanism of the kindreferred to, the photo electric means is sensitive to the speed ofmovement of the bottom of the loop as well as to the actual position andcontrol is exerted accordingly on the speed control means of the strip.By this means a control is effected which is dependent on the rate ofchange of position of the bottom of the loop as well as on the actualvariation in position from the predetermined position so that thecontrol may exert a suitably large force to overcome inertia if thespeed of movement of the bottom of the loop is large. It is furtherwithin the scope of the invention to arrange that the photo electricmeans are sensitive to acceleration or change in acceleration of thebottom of the loop.

In order that the invention may be clearly understood two embodimentsthereof will be described as applied to the loop control of mechanismfor feeding sheet steel strip with reference to the accompanyingdrawings, in which:

Figure 1 is a schematic drawing of the whole of one embodiment of theinvention;

Figure 2 is a detailed view showing the arrangement of the loop, lightand photocell;

Figure 3 is a circuit diagram of the magnetic amplifier referred to inFigure 1; and

2, Figure 4 is a schematic diagram of a further embodiment of theinvention.

Referring to Figures 1, 2 and 3, the steel strip in theform of a loop isindicated at 1 and is located in a light tight pit 2. On one side of theloop in the pit an elongated light source 3 is located, whilst on theopposite side of the pit there is a box 4 enclosing a photocell 5 and. arotating mirror 6. A shield 7 around the photocell, pre;

vents direct illumination from the light source impinging,

on the photocell and limiting the light to that which is refiected fromthe mirror 6. Miror 6 is rotated by a split;

field motor 8 through the medium of a gear box 9. A

further drive from the gear box rotates the movable contact 11 of apotentiometer 12 which is connected across a.

fixed D.C. source. The drive from the split field motor 8 operates atachogenerator 13 which generates a D.C.

plifier 14 of the cathode follower type and the output;

passes to differential servo amplifier 15. The output before being fedinto the amplifier 15, is balanced against, the voltage from a DC source16 through the medium of two resistors 17 and 18. The output of thetachogenerator 13 is also fed into the differential servo am-. plifier.It is thought unnecessary to describe the amplifier 15 in furtherdetail, since it comprises merely two separate thermionic valve D.C.amplifiers, one fed by the output from tachogenerator 13 and the otherfed by the difference voltage from the cathode follower 14 and D11.source 16. The output of the two amplifiers included, in amplifier 15are fed to the two halves 19 and 21 of the field of split field motor 8.These two outputs are ar-, ranged in opposition so that themagnetisation of the field of motor 8. represents an amplified versionof the difierw ence of the two inputs to amplifier 15. The rotor of themotor 8v is fed from a DC. source, 22 of constant value so that rotationof the motor is dependent upon the, direction of magnetisation of thefield.

With the apparatus so far described it is possible to sense the positionof the loop 1, the operation being that if an excess of light falls onphotocell 5, the split field 19 and 21 is energised through amplifier 15tov cause motor 8 to rotate, driving mirror 6 in such a direction thatthe amount of light passing the bottom of the loop and being reflectedfrom the mirror to the photocell is reduced. The output fromtachogenerator 13 provides, a velocity signal, the feed back preventingany tendency for the system to oscillate, whilst at the same time allow:ing the mirror 6 to follow accurately and reasonably quickly the bottomof loop 1.

Movement of the strip forming the loop is controlled by a DC. electricmotor 23 which obtains its-supply of current from two generators inseries, one being a main generator 24 and the other a booster generator25. These two generators are driven from an electric or other motor 26rotating at a substantially constant speed. The booster generator 25includes two field windings 27 and 28 which are energized from amagnetic amplifier 29. The magnetic amplifier 29 is controlled by thevoltage selected by moving contact 11 of potentiometer 12 and the outputvoltage of tachogenerator 13. The magnetic amplifier 29 is shown in moredetail in Figure 3. Power is supplied from the A.C. mains source whichenergizes the primary winding of a transformer 31 having two secondaries32 and 33. The secondary 33 supplies power for a trans, ductor 34 whichis arranged in the well knownmanner to have a pair of main windings 35and 36 fed with alternating current through rectifiers 38 and 39,together with two control windings 41 and 42, an adjustable bias winding43 and a feed back winding 44. The feed back winding is energized by theoutput of a full wave rectifier 45 in series with the alternatingcurrent passing through I Patented May 26, 1 959 the-windings 35 and 36.The output from the tachogenerator 13 is fed to the control winding 41and forms the velocity voltage signal into the amplifier 29. The controlwinding 42 is fed with the voltage from the potentiometer 12 which formsthe position voltage signal. The output from transductor 34 is obtainedfrom a full wave rectifier 46 also in series with AC. supply to thetransductor windings 35 and 36. The output from the rectifier 46 issmoothed by condenser 47 and is fed to two further transductors 48 and49. Both of transductors 48 and 49 are fed from the secondary 32.Transductor 48 includes a pair of half wave rectifiers 51 and 52carrying the alternating current to a pair of windings 53 and 54. Aroundthese windings are located a feed back winding 55, a control winding 56and an adjustable bias winding 57. The feed back winding 55 is fed fromthe output by a full wave rectifier 58 in series with AC. supply towindings 53 and 54, whilst the transductor output is obtained from thefull wave rectifier 59. This output is fed to the field 27. Thetransductor 49 comprises a pair of windings 61 and 62 which are fed fromthe AC. supply through two half wave rectifiers 63 and 64. Around thesewindings 61 and 62 are located the feed back winding 65, the controlwinding 66 and the adjustable bias winding 67. The feed back winding isfed from the output of a full wave rectifier 68 in series with the AC.supply to the windings 61 and 62. The output from the transductor 49 isobtained from the full wave rectifier 69 in series with the AC. input,the output of this rectifier being connected to field 28. The controlwindings 56 and 66 of transductors 48 and 49 are connected in series andfed with the output from transductor 34 which appears as the D.C. outputof full wave rectifier 46.

The whole magnetic amplifier operates in efiect as a push-pullamplifier, the D.C. supply to one field increasing as the supply to theother field decreases and Vice versa. Control is effected jointly by thecontrol windings 41 and 42.

In-operation, whilst the loop is moving the mirror 6, as previouslyexplained, continuously seeks an equilibrium position to allow a certainamount of light to impinge on photocell 5. Signals of the position andangular velocity are fed to the control windings 42 and 41 respectively.If, for example, the strip drive motor 23 is supplying strip too quicklyinto the loop and the loop is extending downwardly into the pit at anexcessive speed and is approaching the bottom of the pit, the mirror 6will move angularly at an equivalent velocity to the movement of thebottom of the loop, whilst the angular position of the mirror indicatingapproach of the loop to the bottom ofthe pit will be indicated by theposition signal to control Winding 42. The position voltage signal willthen be very small and the velocity signal large and will be such thatthe fields 27 and 28 are energized to produce a voltage on the boostergenerator which opposes the voltage of the main generator and reducesvoltage supply to the motor 23 to a minimum to reduce its velocity andhalt downward movement of the loop. If on the other hand strip is beingtaken from the loop more quickly than it can be supplied by motor 23,the loop bottom will rise and approach the top of the pit. The positionsignal voltage given to the amplifier will then increase, whilst sincethe loop is moving upwardly the output of the tachogenerator will bereversed in polarity from that effective in the last example. The effectof the magnetic amplifiers is then to entirely reverse the energizationof the fields from that in the last example and the output from boostergenerator 25 will now be such as to add to the output from generator 24to cause motor 23 to rotate as quickly as possible in order to cause thebottom of the loop to move downwardly into the pit. The whole apparatuswill give automatic adjustment of the speed of the motor 23 inaccordance with the speed at which the strip metal is taken from theloop. The equilibrium posi tion is arranged to be substantially centralof the depth of the pit but, of course, some variation will occur byreason of the speed of strip movement and the necessity to causecorresponding energization of the booster field. Where the motor 23 actsto unwind a reel of strip, whose diameter gets smaller as the strip isused, the control is found to be extremely effective.

Referring now to Figure 4 of the drawings, the loop 1 and pit 2 aresubstantially as previously described. The difference is in the locationof the photocell and the means for sensing the bottom of the loop. Alight strip 3 is employed as in the previous example, but the strip isenclosed in an opaque cylinder 71 having a helical slot 72 extendingaround it for approximately 360 extending the length of the cylinder.The cylinder is mounted in bearings 73 and 74 and is rotatable by meansof a bevel gear drive 75. The bevel gear drive is rotated by a gear box9 substantially as set out in the previous embodiment. All furthercontrols of operation are as set out in the previous embodiment, andmovement and position of the bottom of the loop are sensed by rotationof the cylinder 71 to the position which allows light to pass from theslot over the bottom of the loop to the photocell. It will be seen thatin the normal position of equilibrium the slot will move to a positionwhere a small amount of light only passes the loop bottom to thephotocell and in any position of the loop where the full amount of lightfrom the slot facing the opposite wall of the pit can impinge on thephotocell will result in movement of the cylinder so that the effectiveportion of the slot is lifted.

Many other arrangements of the invention are possible, in particularvariations are possible in the sensing by the photocell of the bottom ofthe loop and in the electrical control mechanism which controls thespeed of movementof strip into the loop. It will be seen that by using asig 11211 of velocity of the loop bottom in conjunction with a signal ofposition it is possible for the control to anticipate dangerouspositions of the loop where it might contact the bottom of the pit oralternately move entirely outof the pit.

We claim:

1. A strip material movement control apparatus comprising strip deliverymeans, strip receiving means, a variable speed driving motor for thestrip delivery means to maintain a downward loop under gravity betweenthe delivery and receiving means, a photo-electric means to generatesignals in accordance with the position and the vertical velocity of thebottom of the loop and a control for the variable speed motor energisedby said signals to adjust motor speed to cause the bottom of the loop tomove to a predetermined vertical position and to tend to reduce verticalvelocity of the bottom of the loop away from the predetermined position,said photo-electric means comprising a photo-electric cell, a lightsource, a servo controlled light directing means to adjust flow of lightfrom the source to the photo cell over the bottom of the loop, a servocontrol energised by light falling on the photo cell to adjust the lightpassing over the bottom of the loop and falling on the photo cell to apredetermined amount and position and velocity signal generatorsoperated by the servo controlled light directing means. i

2. A strip material movement control apparatus as claimed in claim 1,wherein a light source is disposed on one side of the loop and the photocell on the other, the servo controlled light directing means comprisinga pivotally mounted mirror and a servo motor to rotate the same.

3. A strip material movement control apparatus as claimed in claim 1,wherein the light source is elongated in the vertical direction and isdisposed on one side of the loop, and the photo cell is disposed on theother side, the servo controlled light directing means comprising aslotted member and a servo motor to move the member so that the slotposition is variable to vary the light falling on the photo cell.

4. A strip material movement control apparatus as claimed in claim 3,wherein the slotted member comprises a rotatably mounted cylindersurrounding the light source and having a helical slot which duringrotation selects different parts of the source to direct light on to thephoto cell.

5. A strip material movement control apparatus comprising a stripdelivery means, strip receiving means, a variable speed electric motordriving the strip delivery means to maintain a downward loop undergravity between the delivery and receiving means, a light source, aphoto electric cell, a servo controlled light directing means to controlflow of light from the source over the bottom of the loop to the photocell, a servo control responsive to the signal generated in the photocell to adjust the position of the light directing means so that thebottom of the loop reduces the light falling on the photo cell to apredetermined amount, a position signal generator driven by the lightdirecting means to generate a signal dependent on position of thelatter, a velocity signal generator driven by the light directing meansto generate a signal in accordance with the speed of the latter, and aspeed control for the electric motor to tend to cause the bottom of theloop to move to a position where the position signal generator will givea predetermined signal which itself would cause no further movement ofthe loop and to tend to reduce the velocity of the bottom of the loop asindicated by the velocity signal away from the said position.

6. A strip material movement control apparatus as claimed in claim 5,wherein the speed control of the variable speed electric motor isoperable in response to the sum of the position and velocity signals.

7. A strip material movement control apparatus as claimed in claim 6,wherein the position signal generator comprises a potentiometer whosesliding contact is connected for movement with the servo controlledlight directing means to select a voltage signal and the velocity signalgenerator comprises a tacho generator driven by servo controlled lightdirecting means to generate a voltage signal proportional to speed ofthe latter.

8. A strip material movement control apparatus as claimed in claim 7,including a magnetic amplifier to control the electric motor speed andwherein the two voltage signals are fed to individual control windingson the amplifier.

9. A strip material movement control apparatus as claimed in claim 8,including a constantly driven generator Whose output feeds the variablespeed motor and field windings for the generator energised by the outputof the magnetic amplifier.

References Cited in the file of this patent UNITED STATES PATENTS2,393,015 Bendz I an. 15, 1946

